Data about the top and bottom altitude, depth from land surface and/or the thickness of three geologic units in Tennessee were converted into geospatial format for this USGS data release from previously published paper maps and converted into digital formats for use by the public. The three geologic units were the Chattanooga Shale of Mississippian-Devonian age (Moore and Horton, 1999), the Wells Creek Dolomite of middle Ordovician age (Smith, 1959), and the Knox Group of lower Ordovician age (Newcome, 1954). These geologic units represent important geologic horizons across Tennessee. Geologic structure maps provide important information and, in digital format, support investigative and modeling efforts pertaining to water and mineral resources. Prior to this work, the paper source maps used for this data release existed in limited quantities, mainly restricted to the Nashville, TN offices of the Tennessee Department of Environment and Conservation (TDEC) and United States Geological Survey (USGS).
The work for this project included (1) scanning and georeferencing original paper maps to create georeferenced images (GRI), (2) digitizing well location points and contour lines, (3) populating well and contour attribute tables with data from maps and associated reports, and (4) when possible, interpolating raster surfaces for the three geologic units of top and bottom altitude, depth from land surface to the top and bottom surface, and thickness. All raster surfaces were aligned to a modified version of the National Hydrogeologic Grid (Clark and others, 2018) to support USGS Lower Mississippi Gulf Water Science Center efforts to create a statewide hydrogeologic framework. All horizontal coordinated data are projected to NAD 1983 USGS Contiguous USA Albers. The raster vertical coordinate information was referenced to the North American Vertical Datum of 1988 (NAVD 88).
This data release includes GRIs, vector data of the wells and mapped contours of top, bottom, or thickness, raster data, and related metadata files for each three geologic units under the associated child item tab.
